Long established as a science fiction staple, the “tricorder” device popularized by Star Trek has been a dream of many engineers and scientists.
The appeal lies in having the ability to perform medical assessments without contact or intrusion into the patient and the ability to analyze its external environment remotely.
A new device using microwaves and ultrasound technology may be the next step closer to the development of a Star Trek-style tricorder that can “hear” hidden objects.
The device operates using thermoacoustics, the principle that all materials will expand and contract when stimulated by electromagnetic energy such as light or microwaves.
This expansion and contraction produces ultrasound waves that travel through the surrounding medium to the surface and can be detected remotely.
The research team at Stanford University faced challenges involving the rate of expansion and contraction depending on the material’s properties.
Sound waves also propagate differently through solid materials and through air with a drastic transmission loss when sound jumps from the solid to air.
The research team built a capacitive micromachined ultrasonic transducer (CMUT) specifically capable of discerning the weaker ultrasound signals that jump from the solid surface through the air to the detector located a short distance away.
“What makes the tricorder the Holy Grail of detection devices is that the instrument never touches the subject," said Amin Arbabian, assistant professor at Stanford. "All the measurements are made through the air and that's where we've made the biggest strides."
The project originated from a DARPA challenge seeking a system to detect plastic improvised explosive devices (IEDs) buried in the ground. These are currently not visible to the metal detectors commonly used to locate explosive devices.
The primary caveat of the challenge was that the detection device could not touch the surface in question, as that would trigger an explosion.
The Stanford researchers began with this goal in mind, but as their project progressed they began believe their device could become a new way to detect cancerous tumors in the human body.
The team described a potential battlefield scenario where the device could detect buried IEDs in muddy ground.
Since the water-soaked ground will absorb more heat than plastic will, the device’s microwaves would heat the suspect area, causing the ground to expand and squeeze the plastic.
Pulsing the microwaves generates ultrasound pressure waves that could be detected and interpreted to indicate the presence of plastic explosives.
The team’s ultimate goal is to develop the technology into a remote medical device that can perform diagnostics and other medical functions remotely, without touching the patient’s skin.
To test this application, the team implanted a sample “target” into a flesh-like material, then heated it with microwave pulses.
The device operated from approximately a foot away from the material’s surface and the heating level was only a thousandth of a degree – well within safety and comfort limits.
Even that slight amount of heating caused the material to expand and contract, creating ultrasound waves that the Stanford team was able to detect to disclose the location of the target. It all happened without touching the "flesh," just like the Star Trek tricorder.
"We've been working on this for a little over two years," said research professor Khuri-Yakub. "We're still at an early stage but we're confident that in five to ten to fifteen years, this will become practical and widely available."
Prior medical research shows that tumors grow additional blood vessels to nourish their growth. Blood vessels absorb heat differently from surrounding tissue, so tumors should show up as ultrasound hotspots.
"We think we could develop instrumentation sufficiently sensitive to disclose the presence of tumors and perhaps other health anomalies much earlier than current detection systems, non-intrusively and with a handheld portable device," Arbabian said.
Moreover, the researchers believe that their microwave and ultrasound detection system will be more portable and less expensive than other medical imaging devices such as MRI or CT and safer than X-rays.
This could revolutionize medical diagnostics, making accurate diagnostic tools affordable and portable for use in areas with little infrastructure or access to the hospitals and large medical facilities that are currently the only places to access medical imaging and diagnostic systems.
The team’s research is published in Applied Physics Letters and is available to read here.